Although recent advances in genomics have revealed a tremendous amount of nucleotide polymorphism, little is known about why genes segregate for variants that influence quantitative traits. This proposed research seeks to determine which evolutionary processes influence natural genetic variation for complex traits. In order to identify and interpret allelic variants underlying QTLs, this experimental system has four fundamental characteristics: 1) An ecologically important complex trait, 2) a clonable QTL in a known pathway, 3) undisturbed environments where fitness can be measured, and 4) undisturbed populations which retain sequence signatures of temporal and geographic history. These evolutionary analyses use biochemistry to connect genotype with phenotype, and use natural environments to measure fitness. Nevertheless, the fundamental justification for this work is to test hypotheses regarding the evolutionary processes which influence complex trait variation. Towards this goal, a QTL will be cloned which influences ecologically important quantitative variation. Near isogenic lines with better than single gene resolution will be used to measure the fitness and phenotypes of functionally divergent alleles grown in their natural environments. Finally, sequence variation will be used to infer historical and evolutionary influences on allelic variation in undisturbed populations. Public Health Relevance: This proposed research will contribute to our understanding of complex trait variation, which is one of the primary causes of human disease. In addition, these experiments examine the genetics of glucosinolates, which are a focus of biomedical research due to their role in prevention of many forms of cancer, as well as gastritis attributable to Helicobacter pylori.